According to the U.S. National Institutes of Health, approximately 500,000 Americans have Parkinson's disease (PD), with roughly another 50,000 receiving new diagnoses each year. 70%–90% of these people also have the hypokinetic dysarthria associated with PD. Deep brain stimulation (DBS) substantially relieves motor symptoms in advanced-stage patients for whom medication produces disabling dyskinesias. This study investigated speech changes as a result of DBS settings chosen to maximize motor performance. The speech of 10 PD patients and 12 normal controls was analyzed for syllable rate and variability, syllable length patterning, vowel fraction, voice-onset time variability, and spirantization. These were normalized by the controls' standard deviation to represent distance from normal and combined into a composite measure. Results show that DBS settings relieving motor symptoms can improve speech, making it up to three standard deviations closer to normal. However, the clinically motivated settings evaluated here show greater capacity to impair, rather than improve, speech. A feedback device developed from these findings could be useful to clinicians adjusting DBS parameters, as a means for ensuring they do not unwittingly choose DBS settings which impair patients' communication. 1. Introduction 1.1. Background Parkinson’s disease (PD) is an idiopathic neurodegenerative disease caused by loss of dopamine-producing cells in the substantia nigra of the basal ganglia, affecting over one-half million people in the U.S., most over age 50. Its major symptoms are muscular rigidity, bradykinesia, resting tremor, and postural instability. An estimated 70%–90% of patients with PD also develop speech or voice disorders [1] specifically hypokinetic dysarthria [2, page 174]. Hypokinetic dysarthria is characterized by monopitch, monoloudness, underarticulation, and harsh and/or breathy voice. It worsens with disease severity and duration [3] so that patients who are more incapacitated and more reliant on caregivers are also more difficult to understand. The major treatment for Parkinson’s disease is L-dopa, a dopamine precursor given orally to patients. L-dopa is most effective on the general motor symptoms of PD, with variable effects on speech. For example, some studies [4] have found that though motor performance, vocal tremor, and glottal vibration were improved in patients with PD after taking L-dopa, there were no significant improvements in prosody, articulation, or vocal intensity after medical therapy. Other researchers [5] have assessed the amount of pause
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